if i was to spray paint fibreglass, what kind of primer do i need, what type of paint? (just to practise with, maybe waterbased?)

a friend was telling me theres a kind of sealer you need to spray in the fibreglass first to stop the resin reacting with the paint, and then prime, them paint.

if my fibreglass is already painted though, can i just key it, and put primer over that?

A good two pack primer will take straight on to gel or grp that's been properly sanded and dewaxed. Preferably epoxy based, as this will seal the surface.

That's how it's been done on boats for donkeys years, and even the way they do the Aston Martin panels made but a mile or so from me.

Cheers,
Syd.

Cellulose primer and paint will work fine with fibre glass. Just make sure the surface is grease free and well flatted.
Probably the cheapest way as well.

thats guys! the guy that told me about sealing it first has be working on cars as a hobby for years and years and years, so not sure what kind of paint he was thinking

Just spray gelcoat. It sprays well if you buy sprayable stuff, or add acetone to normal stuff. That way, you just have to abrade, degrease then spray! Plus, if you scratch it, the colour goes all the way through!

Shouldn't that be flowcoat? If you spray gelcoat unless it's in an air-free environment it won't go off...

Flow coat is effectively gelcoat with wax solution added. You would only need that for the topcoat. It prevents the surface from remaining tacky when finished.

can you do interesting clours with gel/flow coat? like metallics or paint flips? gelcoat on fibreglass always looks plastic to me...

You can do metallic, but it is not the same depth of colour as paint due to the lack of laquer. Flip paints - kinda. Have a look here.